Pneumatic size gauging device



Patented Aug. 14, 1951 PN EUMATIC SIZE GAUGING DEVICE -Andr Louis Aim Fortier, Grenoble, France, as- `signor to Etavex -S. A., a corporation of Switzerland Application September 4, 1947, Serial No. 772,105 In 'Switzerland July 18, 1947 1- Claim.

vIt is known that it is possible to measure the distance between two adjacent surfaces by means of a iiow of gas. For this purpose one of the surfaces is pierced with a small oriiice through which va gas flows. When the other surface is approached towards the oriice, the free cross section afforded to the passage of the gas depends on the distance'between the two surfaces. Under-these conditions, the measurement ofthe outiiow-of -gas or of the pressure at the upow of the oriiice enables the distance between vthe .two surfaces to 'be determined. In particular when av calibrated orifice of constant cross section is placed in series with the orifice of variable section, Yaccordingto theposition of the two surfaces, .the vmeasurement of -the resulting pressure .p between the-two surfaces enables the free cross section of the `second orice to be 'determined when the pressure is maintained at a-given value P atthe .upflow of the rst orice and when the pressure .at the downiiow of .the second orifice is known, .whichimay be simply atmospheric pressure ma. When the differences vin the -pressures P-,p and p-poare small relatively to the pressures P, p and 100, the deliveries Q1 through the iirst orice and .Q2 .through -the second orifice are proportional to thelpowersof `P-p andvp-po which vary from l.1 .to 1/2 according to rthe geometrical .shape-of the cross sections of the two orifices. When equilibrium-is established the deliveries Q1 and Q2 are equal. Under these conditions, whenthe pressure P andpo are constant, the discharge -through the-upflow .oriiice being constant, thepressurep is a function of the magnitudeof the section,oriiiceandenablesit to be measured aftera previous marking by. a standard. The second .orilice may be located-at a distance d froma wall.p is thus the function ofv :Zand the measurement of p enables .d'tobe found.

For obtainingcorrect results, itis necessaryto maintain .the pressure Pconstant by. means of a pressure regulator or anexpandingdevice located on the 4up'iiow .of .the rst'orice.

. But theemp'loyment of known .pressure regula- -tors involves dilculties. .The most precise, of the type provided witha container filled with liquid toa constant level into which dips a. stationary gas Yinlet tube, are fragile and of little practical use for commercial measurements. The same applies to liquidfgauges. VRegulators or ordinary metal -gauges lack sensitivenesa accuracy and precision.

Ithasbeen proposed, for remedying these disadvantages, to measure the resistance opposedby an oriiice. to .thepassage of i a gas,not directly by 2 the measurement Aof a pressure p, but by comparison with a known resistance.

One'of the best mountingslknown, for eiecting this measurement of comparison, is that shown in Fig. 1 in a diagrammatic manner. It is the equivalent in the fiieldof mechanics of iiuids, to the Wheatstone bridge commonly utilised for the measurement of electrical resistances.

The main branches I and 2 of this Vbridge are connected at 3 fto va vtank of relatively constant pressure P. From the'point-cf connection 3, each branch is provided with twoorifces 4, 5 and B, I respectively, resisting the Iiow of gas -and arrangedinfseriesjthe intermediate sections of the Ibranches 'forming chambers 8 and 9 between which is located `the bridge -IU proper, provided with a `dilierential gauge I Iyalso serving to indicate equality in pressure. The measuring'orilice 'I is located in proximity to a wall b, while a movable needlev40 enables the useful cross section to be modied, that is to say the Yresistance of the comparisonforice V5.

The principal advantage of this assembly of Wheatstone bridge 'is'to render the precision of the measurements liable to be influenced only very -slightly by the lvalue of the pressureP at the upflow and Vbythe temperature, so'that it is the samein'all'the parts of the apparatus.

But in order'that the measurementbe precise and independent of 4P,it isnecessary thatthe gauge II, for-indicating equality in pressure, be Very sensitive. It is necessary, more exactly, for thegauge v4I I to be sensitive to the smallest difference which might exist between thev pressures in the chambers 8 and 9. It is forthis reason that it'has been proposed theretofore to use as an indicator of equality in pressure between the chambersafliquid gauge with'inclined tubes. Besides its iragility,'such a gauge has-another serious disadvantage before resistances through the orifices 5 and I are equalized under the influence of pressure P. Such inequality of pressure causes the liquid to be emptied from the gauge. It is therefore necessary to provide a tap or bleeder to stop the iiow of gas to the sensitive indicator II while the resistance 5 is adjusted so as to obtain approximate equality of pressures in the spaces 8 and 9. This tap plays the part Vof the .switch of the electric Wheatstone bridge which only enables current to be passed through the sensitive galvanometer when equilibrium of the bridge is already almost obtained. The operation ithis tap, which is indispensible and which, however, hasnot been provided in the assemblies described so far, renders the apparatus practically useless commercially.

Instead of the liquid gauge with inclined tubes, it is possible to use a metal or mechanical gauge of a known type. In this case, although the gauge may resist a considerable difference in pressure, it is necessarily only slightly sensitive and consequently does not aiiord the full advantages of the Wheatstone bridge assembly. On the other hand, if the gauge is very sensitive and consequently fragile it is necessary to protect it in such a manner that the large differences in pressure which exist between the chambers 8 and 9 during the adjustments are not liable to damage it.

The present invention has for its object the provision of a differential pressure indicating device with a deformable diaphragm secured at its periphery or rim and separating two gas chambers, applicable to a measuring assembly similar to that shown in Fig. 1. This device is distinguished from other known devices in that it is provided, in combination with a Wheatstone bridge assembly, with at least one bearing surface for limiting the maximum deformation of the diaphragm under the action of a resultant pressure, that is, limiting the movement of the diaphragm so that it will not become damaged and will return to its original neutral position, this bearing surface being so shaped that, practically, the whole of the useful surface of the diaphragm can be applied thereto.

Such a device can resist, without damage, the large dierences in pressure while retaining its sensitiveness when the pressures are equalized.

In the accompanying drawing:

Fig. 1 is a diagrammatic view illustrating the application of the invention to a measuring assembly.

Fig. 2 is a cross sectional View of one embodiment of the invention and Fig. 3 is a similar sectional View of another embodiment.

I'he parts common to both embodiments will be first described.

A connecting tubular member I2 is connected at'one end to an air tank, not shown, in which is maintained a substantially constant pressure P, appreciably higher than atmospheric pressure. The other end of the tubular member is connected to two passages I3 and I4 in shunt, said passage containing calibrated orifices I5 and I5, assumed identical for simplification of the description. The passages I3 and I4 are provided in a casing I1.' 'The passage I3 leads into a chamber I 8 communicating with the atmosphere through a calibrated downiiow oriiice I9 provided in a plate 2l! covering the chamber I8; the passage I4 leads into a smaller chamber 2I communicating with the atmosphere through a second calibrated orifice 22.

A differential pressure indicating device, described hereinafter, is interposed between the pneumatic chambers I8 and 2l, which are the equivalent of the respective chambers 8 and 9 of the Wheatstone bridge assembly shown in Fig. 1.

Into the bottom of the chamber I8 is fitted an annular iiuid-tight lining 23. A dished or concav-e circular trough 24 is secured in a fluid-tight manner` to the lining 23 at its lower edge 25 projecting from the under face 26 of the said trough 24. Consequently the under face 26 is located at a predetermined distance from the bottom of the chamber I8. The trough 24 is provided with a number of perforations 21 distributed uniformly and its upper edge is flat; it serves to support the periphery or rim of a circular diaphragm 29 normally flat and equally deformable by pressure from either side thereof.

A second trough 39, substantially similar to the iirst, but inverted and provided with perforations 3I, is disposed on its iiat lower edge 32 to the periphery or rim of the diaphragm 29 which is thus clamped between the two troughs and secured to the casing I1 by securing means not shown. Y

The concave surfaces of the two troughs 24, 30 are located opposite one another and also have the same axis of rotation 2-z, coincident with the axis of symmetry of the diaphragm. These concave surfaces are so shaped that they form bearing surfaces for practically the whole of the effectively deformable portion of the diaphragm.

The diaphragm 29 carries at its center a, boss 33 'secured to a rod 34 passing freely through the upper trough 30 and connected to a resiliently iiexible contact bar 35 of which one end is connected to a terminal 36; The free end of the contact bar 35 is located between two conducting blades 31, 38 clamped in an insulating block 39, but does not touch either when the located diaphragm 29 is in neutral position.

The calibrated orifice 22 opens at a short distance d from an object b, the dimensions of which it is desired to measure.

The free cross section of the second orifice is modified by an axially movable needle or valve stem 40.

All the members which have been described with reference to Fig. 2 occur in the same manner and similarly combined in the apparatus shown in Fig. 3. They form a kind of pneumatic Wheatstone bridge.

The apparatus of Fig. 2 which serves to measure automatically, for example, the variations in thickness of a rod b, seen in end View resting on a support M that the operator moves longitudinally, is also provided with a reversible or electric servo-motor 4I with two directions of rotation of which the field windings, of opposite direction, are connected to blades 31 and 38, respectively. One pole of the source of current S is connected directly to the terminal 42 of the motor. The other pole is grounded to the casing I1 by a lead 43.

A pinion 44, mounted at the end of the shaft of the motor 4I meshes with long internal teeth of a transmission flange 45 which is rotatable about and slidable along the axis 22. The hub 46 of the fiange 45 has a screw thread engaging with a screw-threaded bore 41 of a cover plate 20. The iiange 45 carries on its outer edge a scale 48 movable under a stationary pointer 49.

The apparatus is used as follows.

As the horizontal support M is adjustable in height, it is placed in such a position that the distance d of the calibrated orifice 22, from the upper face of the rod b determines for this orifice a free cross section for the passage of air of the same resistance as that opposed by the orifice I9 into which the needle 40 has been moved previously into an arbitrary zero position marked by the scale 48.

The operator moves the rod b longitudinally on the support M. When its thickness varies the distance d likewise Varies and the free cross section for the passage of air through the orifice 22 is modified which, in turn, modifies the pressure in the chamber 2I acting on the lower face of ausg-a? the diaphragm '29. Whenfforexample, a lowering of the sensitive pressure-occurs, the said diaphragm-.curves downwardly-towards thezbottom v:and its useful surface bears'almost overfitscen- .tire area .-.against the concave rsurfacefiof 'the .trough l 24 which serves as Aa :support Ytherefor whilefavoiding any deleteriousurging offthefdi- .aphragmfunder the action .of .the diiTerence 1in `pnessurebetween the chamber-S48 and 'f2|,that ian-avoiding movement :of the diaphragm :beyond its elastic limit. When curving in this manner, the diaphragm carries with it the bar 35 which closes the circuit of the motor 4| by coming into resilient contact with the blade 38. The motor 4| starts, causing the flange 45 to turn, which produces an axial ascending movement of the needle 4D in the orifice 9 until the resistance opposed by this orice has become equal to that opposed by the orifice 22 opposite the bar.

Equilibrium of the pressures between the chambers I8 and 2| is thus re-established, the diaphragm resumes its mean or neutral position, seen in Fig. 2, and the bar 35 moves away from the blade 38. The circuit through members 42, 4|, 38, 35, 3B troughs, casing and lead 43 being broken, the motor 4| stops. During the rotation of the motor 4|, the scale 48 has turned under the pointer 49 by an amount which is a function of the variation necessaryy of the cross section of the orice I9 for re-establishing equilibrium of pressures between the chambers I8 and 2 This quantity, read directly on the scale, indicates to the operator how much the distance d has increased and, consequently, how much the thickness e of the bar has decreased, relatively to the thickness of the bar in its initial position.

Conversely, when the thickness increases between two successive positions of the bar b, the

pressure increases in the chamber 2|, the diaphragm curves upwardly until it bears against the trough 36. The bar 35 closes the circuit of the motor by contacting the blade 3l, the motor 4| starts in a direction opposite to its previous direction of rotation, until pneumatic equilibrium is re-established between the chambers I8 and 2 The diaphragm 29 returns to its mean or neutral position and breaks the circuit between the blade 39 and the bar 35. The new position assumed by the scale 48 behind the marking pointer 49,

enables the increase in thickness e of the bar b to be ascertained from the region measured previously. In continuing the movement of the bar in this manner, then stopping it each time the motor 4| starts until the motor stops automatically, it is possible to measure the variation in thickness of the bar over its entire length in a semi-automatic manner.

Even when, involuntarily, the bar is moved suddenly from the orce 22, the sudden lowering of pressure then produced in the chamber 2| is not liable to damage the diaphragm 29 which simply bears over its entire useful surface against the concave surface of the lower trough 24. The perforations 2l have too small a diameter to enable a thrust of sufficient value to pass therethrough for damaging the diaphragm even when it is thin and therefore sensitive.

In the apparatus shown in Fig. 3, and which may serve for measuring the dimensions of an object b or of a series of objects, the needle 40 is secured to an operating knob 5| of which the threaded spindle 52 engages with a screw threaded bore 4l of a cover plate 2D. The conducting blades 3l and 38 are connected to two different circuits 1153, l'54 in lparallel in y a fdistr'ibuting fnetwork-S. Inla very zsimplefexamplathese `circuits may be formed by signalling lamps ofdifferent colors. It will at once be seen that a variation 'of therdimension of1an-object b producing an increase of pressure in the chamber 2| is translated by curving of the diaphragm 29 upwardly and bythe:closingsofcontacts 35, 31 resulting-in vthe lighting vofathe-lampz53. The operator then actuates the knob -5| in such `a direction that the needle 48 penetrates considerably into the orifice I9, until the lamp 53 is extinguished, indicating the return of the diaphragm 29 to the neutral or mean position and the re-establishment of equilibrium of the pressures in chambers I8 and 2|. Reading the scale 48 gives the new value of the distance d, and therefore, the variation in dimension of the object b.

If it is the lamp of the dimension of direction.

It will be understood that the possible applications of the invention, are numerous, the applications shown in Figs. 2 and 3 being illustrations 54 which lights, the variation the object b is in the opposite only. In particular the device may be applied to the automatic control, for example, of a truing device. In using the device shown in Fig. 3 for this purpose, the contact blade 31 is omitted, because the truing machine, such as a grinding wheel, operates only to shorten the dimension. Consequently, control in only one direction is necessary.

From the foregoing description it will be seen that the invention has, among others, the following technical advantages:

1. The possibility of operating at a high pressure, while using a very pliant diaphragm which is very sensitive to small differences in pressure, at the same time being resistant to great differences in pressure between its two faces, which makes it possible to take full advantages of a Wheatstone bridge assembly.

2. The provision of an apparatus of very small dimensions which responds very rapidly to variations in dimensions of the object to be measured or controlled. In fact an extremely rapid reaction of the apparatus is obtained by reducing the effective volume of the gaseous medium located on the downstream of the orifice I6, by placing this orice at the outlet of the passage I4 in a cylindrical cavity forming the chamber 2 I claim:

A pneumatic gauge comprising a casing having a pair of separate gas chambers therein, said chambers having a common wall consisting of a yieldable diaphragm, a pair of perforated concave members straddling and holding the rim of said diaphragm against axial movement, said concave members being also adapted to limit the axial displacement of the center of the daphragm, each of said chambers having a gas inlet, means for delivering a gas under pressure to said inlets from a common source, each of said chambers having also an outlet, the outlet of one chamber being adapted to be disposed in proximity to a surface of an object to be gauged, the other outlet having valve means therein, means including an external rotatable member for actuating said valve means, a scale carried by said rotatable member, a stationary pointer adjacent said scale, a double throw electrical switch having a movable element, said element being connected for movement with the center of said diaphragm, a reversible electric motor mechanically geared to said rotatable member,

said switch being electrically connected t0 Said Number motor. 2,125,949 2,216,374 ANDRE LOUIS AIME FORTIER. 5 2,266,556 2,347,590 2,350,058 REFERENCES CITED 2,352,312 The following references are of record in the 2,390,252 le of this patent: 10 2,516,932

UNITED STATES PATENTS Name Date OConner Aug. 9, 1938 Martin Oct. 1, 1940 Poole Dec. 16, 1941 Binder Apr. 25, 1944 May May 30, 1944 Donaldson June 27, 1944 Hayward Dec. 4, 1945 Wainwright Aug. 1, 1950 

